1. Field of the Invention
Illustrative embodiments of the present invention relate to an inkjet recording apparatus, and more specifically, to an inkjet recording apparatus capable of preventing negative pressure in a head tank from being completely lost during a standby time after ink ejection.
2. Description of the Background
Inkjet recording apparatuses generate energy using an energy generation unit, such as a piezoelectric element mounted on a liquid chamber of a recording head, to eject droplets of liquid, e.g., ink stored in the liquid chamber from ink nozzles provided in the head to form an image on a recording material. Inkjet recording apparatuses are widely used because of their cost-effectiveness and compact sizes. Below, one conventional type of inkjet recording apparatus is described with reference to drawings.
FIG. 12 is a schematic view illustrating a configuration of an ink-supply tube system in a conventional inkjet recording apparatus. As illustrated in FIG. 12, the conventional ink-supply tube system connects an ink cartridge 11 containing ink to a head tank 14 via a liquid-feed pump 12 and a supply tube 13 and employs in the recording head a single tube configuration for different colors of ink, e.g., black, cyan, magenta, and yellow. As ink stored in the head tank 14 is consumed for printing or maintenance, the liquid-feed pump 12 supplies (refills) ink from the ink cartridge 11 through the supply tube 13 to the head tank 14.
In such an inkjet recording apparatus, for example, the following maintenance operations are performed:
1. cleaning (optional/automatic) for restoring slightly clogged nozzles;
2. refreshing (optional) for restoring clogged nozzles not recovered by cleaning; and
3. air-releasing and refilling (automatic) for creating negative pressure in the head tank if the negatively pressurized state of the head tank is lost.
Cleaning and refreshing are performed to restore nozzles to optimum conditions, thus requiring a certain amount of ink to be discharged from the nozzles. By contrast, air-releasing and refilling operation is performed to create negative pressure in the head tank 14, that is, change the volume of the head tank 14, thus requiring no ink to be discharged from the nozzles.
FIG. 13 is a perspective view illustrating a configuration of the head tank 14 shown in FIG. 12. A negative-pressure lever 14-1 is mounted on the head tank 14 and moved by a film 14-2 that deforms as ink stored in the head tank 14 is consumed. The head tank 14 is negatively pressurized by a spring, not illustrated, which is provided in the head tank 14 to bias the film 14-2. Ink is supplied from an ink cartridge via an ink supply tube through a supply port 14-3. An air-release pin 14-4 is a pin with which the interior of the head tank is opened to the atmosphere when needed. At a lower portion of the head tank 14 is mounted a recording head 14-5 that ejects ink droplets. A detection unit 14-6 is provided to detect ink and air.
In creating negative pressure in the head tank 14, as illustrated in FIG. 14, ink is discharged from head nozzles 15 with a suction cap 21 covering the head nozzles 15. As a result, the internal volume of the head tank 14 changes, thus deforming the spring in the head tank 14. Ink discharged from the head nozzles 15 is suctioned by a suction pump 22 and received in a waste-liquid tank 23.
In such inkjet recording apparatuses, ink is typically supplied from an ink cartridge. However, in replacing the ink cartridges, air may be mixed into a new cartridge, thus causing ink ejection failure. To deal with such a problem, several conventional approaches have been proposed.
For example, in one technique like that described in Japanese Patent Application Laid-Open No. 2005-125667, a liquid ejection apparatus includes an ink supply line through which ink is supplied from the ink tank to the ink head and an ink return line through which ink is returned from the ink head to the ink tank. In the liquid ejection apparatus, ink circulates between the ink head and the ink tank to prevent leakage of ink from the nozzles of the ink head.
In such a conventional liquid ejection apparatus, resin materials may be used in ink passage portions of components, such as the ink cartridge, the liquid-feed pump, the liquid-feed tube, the head tank, and the ink head in the ink-supply tube system. Further, joint portions between such components are formed of, e.g., rubber packing material to obtain high sealing performance.
When the liquid ejection apparatus is in a standby state, the interior of the head tank is negatively pressurized. As long as such a standby state is maintained for a time period that remains within design limits, it does not matter. However, if the standby time exceeds design limits, the negative pressure of the head tank is lost and the interior of the head tank acquires atmospheric pressure. Such loss of negative pressure may be caused by the air permeability of the resin or rubber material and the sealing performance of the rubber packing material. Further, since the interior of the supply tube is negatively pressurized by the head tank, air may be absorbed into the supply tube and as a result the negative pressure of the head tank is lost.
To reduce the air permeability of the materials, for example, it is conceivable to substitute for such resin and rubber materials higher-performance resin and rubber materials or metal materials, or coat the surfaces of components with metal material. To enhance the sealing performance of packing material, it is conceivable to connect joint portions by adhesion, deposition, or fusion, or integrate some components so as to reduce the number of joints.
A further consideration is that, in an inkjet recording apparatus with an ink cartridge containing a great amount of ink, the ink cartridge may be directly mounted on the recording head that is mounted on a carriage. In such a configuration, the weight of the ink cartridge may cause failures in the operation of the carriage, degrading image quality. Hence, in one conventional inkjet recording apparatus, the ink cartridge is mounted on a housing of the inkjet recording apparatus and as illustrated in FIG. 14 a head tank 14 that temporarily stores ink is mounted on the recording head that is mounted on the carriage. In such an inkjet recording apparatus, if ink is fed from the ink cartridge with the ink cartridge out of ink, the negative pressure in the liquid feed passage between the ink cartridge and the head tank increases and air bubbles may get into the liquid feed passage upon installation or removal of the ink cartridge. Such air bubbles may further get into the head tank through the liquid feed passage. At this time, for example, if ink is supplied with the air release valve opened, a combination of air bubbles and ink may leak from the air release valve, causing failures such as damage to the recording head. Further, if such air bubbles get into the nozzles of the recording head, image failures such as non-ejection from a portion of the nozzles may arise.
Hence, to deal with such failures, several conventional approaches have been proposed. In one conventional technique like that described in Japanese Patent Application Laid-open No. 2003-341028, an inkjet printer includes an intermediate ink tank between the ink cartridge and the recording head and a pressure sensor disposed away from the intermediate ink tank. While detecting a negatively pressurized state of the recording head, the intermediate ink tank is elevated up and down to keep a certain negative pressure.
However, a drawback of such an arrangement is that, as the recording head, the intermediate ink tank, and the pressure sensor are disposed away from each other, the system may be complicated and upsized. Further, the system includes such a mechanism of elevating the ink tank to keep a certain negative pressure, thus resulting in upsizing and complicated configuration. Further, if air bubbles get into the intermediate ink tank during replacement of the ink cartridges, it is difficult to remove such air bubbles.
In another technique like that described in Japanese Patent No. 3,269,368, an ink supply device is proposed in which a sub tank having a meniscus formation member is provided with a main tank containing ink. As the pressure in the main tank decreases with ink consumption, ink is automatically supplied from the sub tank by an amount corresponding to the decreased pressure to maintain a certain negative pressure. However, as the meniscus formation member deteriorates, it may be difficult to keep the certain negative pressure. Further, if air bubbles get into the sub tank in replacing ink cartridges, it may be difficult to remove such air bubbles from the sub tank.
In still another conventional technique like that described in Japanese Patent No. 2,898,746, an inkjet pen includes a sealed ink tank containing ink. In the sealed tank, a small hole is formed so that one end of the hole is open to the atmosphere. As ink stored in the ink tank is consumed, air is supplied through the hole into the ink tank to keep a certain negative pressure in the ink tank. However, since the ink tank is always open to the air, air bubbles are more likely to go into the ink tank. Further, if such air bubbles get into a head channel in replacing ink cartridges, it may be difficult to remove such air bubbles from the head channel.